1. Field of the Invention
The present invention relates to the thermo-chemical cleaning of storage tanks used in the oil and related industries, and more specifically, to removing oil sludges from refinery tanks, ship containers or any other storage means for storage and treatment of oil and related products. The new process can equally be used in the removal of oil adsorbed or impregnated on clay or sandy solids such as gravel packing, sands, etc.
2. Prior Art
European patent 032813 describes a process for the removal of sludges from crude or refined oil storage tanks by injecting a dispersing agent into the sludge by means of a water jet. The emulsified oil fractions are removed under pressure and recirculated to the jet. The sludge is physically and chemically altered so that it can be pumped and easily removed from the tank, the emulsion being further mixed to an oil volume sufficient to cause the sludge separation, the water layer being separated and the heavy hydrocarbons recovered.
Japanese publication J 58 030398 describes the treatment of sludges by adding the same amount of solvent and heating by circulating in the oil furnace to extract paraffin waxes and separating solid constituents from the oil fraction.
J. W. Barnett in an article in "Hydrocarbon Processing" issued in January 1980, p. 82-86 entitled "Better Ways to Clean Crude Storage Tanks and Desalters", has described a process for heating sludges by using hot water and emulsifiers in one mode, while another mode uses hot solvent, both modes requiring external means for heating and circulation.
The so-called T.H.O.R. process is a mechanical system for the recovery of hydrocarbons from the oil sludge and contaminated oil tank bottoms. The process involves penetrating the sludge bulk with a hot water circulating system using a submersible pump. The T.H.O.R. process comprises two stages: sludge moving and sludge refining. To render the sludge mobile, water heated with refinery steam is pumped into the tank to lower the viscosity of the sludge so as to optimize its pumping and recovery. The mobile sludge is pumped through a submersible pumping unit placed in the medium to be pumped. The amount of water placed into the tank is equivalent to that of the sludge to be moved. The water is kept circulating during the whole liquification period of the tank contents, which normally takes 7 to 8 days. The pumping process has a maximum flow rate of 15000 liters per hour, the mass being pumped corresponding to a ratio of 50% water/50% sludge. The mixture is pumped through Alfa Laval equipment for the removal of insoluble foreign matter and water so as to produce oil to be reintroduced in the refining process. The recovered product, of BSW lower than 1% and low conductivity is mixed to crude oil in predetermined amounts. The so-called "SUPERMACS" system developed by Riedel Environmental Technologies Inc. employs heated water jets under high average pressure, in order to melt and heat paraffin and sludge deposits. The prducts are separated and recovered based on their different densities, the oil contained in the sludge also being recovered. Thus, to be effective, the processes described in the literature require heating, agitation, solvent and additives, in separate or combined manner. The process of the present invention provides heating in situ free of any energy expense, agitation generated by turbulence and free of agitators, besides a flotation effect caused by the gaseous nitrogen used, without any requirement for externally added gas. Furthermore, flotation, which is unknown in the processes of the prior art, facilitates stratification.